This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-168968, filed Jun. 15, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a particle-measuring system that is mounted on a processing unit for forming a film on a semiconductor wafer by using a gas, and that measures the number of particles included in an exhaust gas discharged from the processing unit.
Generally, in the manufacturing of semiconductor integrated circuits, various kinds of processing units are used for processing semiconductor wafers (hereinafter to be referred to as wafers) as objects to be processed at various manufacturing stages, including a film deposition (CVD: chemical vapor deposition) process, thermal oxidation and impurity diffusion processes, an etching process, a film forming (sputtering) process, a thermal processing process, etc.
In the film forming process, thin films such as a silicon oxide (SiO2) film, a silicon nitride (SiN) film, and the like are deposited as insulation layers or insulation films on the surface of the wafer using, for example, a CVD unit. For forming wiring patterns and embedding trenches, thin films of tungsten (W), tungsten silicide (WSi), titanium (Ti), titanium nitride (TiN), titanium silicide (TiSi), etc. are deposited.
When these processing systems are used to carry out each processing, it is necessary to avoid as far as possible the generation of particles that become the cause of reduction in product yield.
Therefore, a particle-measuring system is installed on the processing system in order to real-time monitor the state of generation of particles within a processing chamber or in order to know the timing for cleaning the processing chamber. Particularly, in the film-forming system such as a CVD system or a sputtering system, there occurs an adhesion of unnecessary films onto the inner wall of the processing chamber or onto the surface of the parts. These unnecessary films are disposed and accumulated within the chamber during the film-forming process. These unnecessary films are easily peeled off at the next film-forming cycle, and particles are easily generated. Therefore, it has been important to monitor the volume of particles generated during the film-forming process.
One example of a processing system having a conventional particle-measuring system will be explained with reference to FIG. 18.
A mounting table 4 for mounting a wafer W is provided inside a processing chamber 2 of almost a cylindrical shape, and a transmission window 6 made of quartz glass is disposed on the bottom of the chamber. A plurality of heating lamps 10 are disposed on a rotary table 8 below the transmission window 6. Heating beams irradiated from these heating lamps 10 are transmitted through the transmission window 6 to heat the wafer W on the mounting table 4.
A shower head 12 for introducing a processing gas such as a film-forming gas into the processing chamber 2 is provided on a chamber ceiling that faces the mounting table 4. Four exhaust openings 14 (only two openings are shown in the drawing) disposed with approximately equal intervals are provided on the periphery of the bottom of the processing chamber 2. Each of these exhaust openings 14 is connected to an exhaust pipe 16 extending downward.
Respective discharge sides of the exhaust pipes 16 are assembled into one, which is then connected to one absorption side of an assembling pipe 20 of a large diameter. A butterfly valve 18 for adjusting pressure is provided inside the assembling pipe 20. A vacuum pump 22 is provided at a discharge side of the assembling pipe 20, and a main exhaust pipe 24 of a relatively large diameter is connected to a discharge side of the vacuum pump 22. Atmospheric air and a gas within the processing chamber 2 are exhausted to the outside by this vacuum pump 22. A particle-measuring system 26 for counting the number of particles included in the exhaust gas is provided in the middle of the main exhaust pipe 24.
FIG. 19 is a diagram showing a cross-sectional configuration of the main exhaust pipe 24 provided with the particle-measuring system 26.
The particle-measuring system 26 has a laser beam irradiator 28 for emitting laser beams L and a stopper 32 for suctioning the emitted laser beams L disposed opposite to each other so that a line connecting between the two units pass through a center O of the main exhaust pipe 24. Further, a scattered light detector 30 for detecting scattered lights SL generated by a collision of the laser beams L against particles P in the middle of the irradiation of the laser beams L, is disposed facing the center O of the main exhaust pipe 24.
Based on this arrangement, for measuring the particles, the scattered light detector 30 detects the scattered lights SL that are generated when the laser beams L irradiated from the laser beam irradiator 28 have collided against the particles P that move within the main exhaust pipe 24. The particle-measuring system 26 counts the number of the particles included in the exhaust gas based on this detection.
According to the above-described conventional processing unit, the particle-measuring system 26 is provided on the main exhaust pipe 24 at the discharge side of the vacuum pump 22 that assembles the exhaust pipes 16 from the processing chamber 2 together. of course, abnormalities of products adhere onto the inner walls of the exhaust pipes and blades of the pump and the valve due to the exhaust that occurs during the process from the processing chamber 2 to the particle-measuring system 26. These adhered abnormalities are peeled off irregularly, and these generate new particles.
As the particles generated irregularly are added to the discharged particles that have actually been generated from within the processing chamber 2, it has not been possible to accurately grasp the number of particles that have been generated from within the processing chamber 2.
Further, the exhaust gas is swirled within the exhaust pipe near the discharge side of the vacuum pump 22. Therefore, the same particles cross the laser beams repeatedly, and they are counted a plurality of times.
In principle, the actual number of particles within the processing chamber 2 should be highly correlated with the count number based on the measurement of particle by the particle-measuring system 26. However, for the above reason, there is a very low correlation between the two data. Therefore, according to the conventional particle-measuring system, it has been difficult to accurately understand the state of particles actually generated from within the processing chamber 2.
It is an object of the present invention to provide a particle-measuring system capable of grasping a state of generation of particles by keeping high correlation between the number of particles generated and exhausted from within a processing chamber and the counted number of particles based on an accurate counting of the number of particles exhausted.
The present invention provides a particle-measuring system mounted on a processing system that has a processing unit for carrying out a predetermined processing of an object to be processed and an exhaust system for exhausting an atmospheric gas from within a processing chamber of the processing unit by a vacuum pump. Within the processing system, the particle-measuring system is installed on an exhaust pipe that forms a part of the exhaust system communicating between an exhaust opening of the processing chamber and the vacuum pump. With this arrangement, the particle measuring system measures the number of the particles included in the exhaust gas discharged from within the processing chamber.
The particle-measuring system is constructed of a laser beam irradiator for irradiating laser beams to within the exhaust pipe so that the laser beams pass along a line connecting between a center point of a cross section of the exhaust pipe and a center axis passing vertically through the center of the processing chamber, and a scattered light detector provided in a direction approximately orthogonal with an irradiation direction of the laser beams, for detecting light scattered from particles.
The present invention also provides a particle-measuring method for measuring the number of particles included in an exhaust gas exhausted from a processing device for generating an atmosphere including atmospheric air or a gas exhausted from within a processing chamber by a vacuum pump, and for processing an object relating to a semiconductor manufacturing in this atmosphere, the method comprising the steps of: modeling parameters; carrying out a numerical simulation for expressing tracks of an exhaust gas that includes particles flowing through an exhaust pipe; carrying out a track numerical simulation of an exhaust gas and particles; confirming an optimum position for measuring particles; determining sensor installation position; installing the sensor; and evaluating a measurement of particle, wherein tracks of particles that flow through the exhaust pipe after the particles have been generated inside the processing chamber and exhausted from the processing chamber are simulated, to select an area where the density of the particles is the highest in the radial direction of the exhaust pipe, a laser beam irradiator is disposed at a position in this area where laser beams for measurement pass through, and a scattered-beam detector is disposed in a direction orthogonal with the laser beams, thereby to measure the particles.
The present invention further provides a particle-measuring method for measuring the number of particles included in an exhaust gas exhausted from a processing device for generating an atmospheric air or a process gas exhausted from within a processing chamber by a vacuum exhaust system, and for processing an object relating to a semiconductor manufacturing in this atmosphere, the particle measuring method using a device having a laser irradiator, a scattered-beam detector and a beam stopper for measuring the number of particles by irradiating laser beams to particles generated within the processing chamber, the particle-measuring method comprising the steps of: selecting an area in which the density of particles is high by carrying out a simulation based on information on constructional members including the processing chamber and other members disposed inside the processing chamber, information on the vacuum exhaust system, and information on the process gas; adjusting a position of the laser beam irradiator so that the laser beam irradiator can irradiate laser beams in an area in which the density of particles is high based on the simulation; adjusting a position of the beam stopper to face the laser irradiator so that the beam stopper can receive laser beams passed through the high-density area; adjusting a position of the scattered-beam detector so that the scattered-beam detector can detect scattered beams of the laser beams passed through the high-density area; irradiating by the laser irradiator the laser beams to an area in which the density of particles is high; detecting by the scattered-beam detector the scattered beams of the laser beams passed through the high-density area; and calculating the number of particles from the scattered beams detected.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.